Trucks forming part of a Russian aid convoy are parked in a field about 4 miles from a border control point with Ukraine in the Russian town of Donetsk, Rostov-on-Don region, Russia, on Aug. 21. / AP

by Doug Stanglin, Michael Winter and Kim Hjelmgaard, USA TODAY

by Doug Stanglin, Michael Winter and Kim Hjelmgaard, USA TODAY

NATO officials said on Friday that Moscow has sent Russian-manned artillery units into Ukraine in recent days and was using them to shell Ukrainian forces as part of a "major escalation" of Russian involvement in the disputed region.

The allegations came as a Russian convoy carrying "humanitarian cargoes" defied the Ukrainian government and International Committee of the Red Cross by crossing the border and arriving in Luhansk, the separatists' stronghold in eastern Ukraine.

U.S. deputy national security adviser Ben Rhodes warned Russia to remove the convoy from Ukraine or "face additional costs and consequences" from the United States and its allies.

Rhodes also condemned the firing of artillery from Russia into Ukraine and a "disturbing movement of Russian artillery and military equipment" into the country.

Friday night, Russia's state-run Itar-Tass news agency announced that the convoy had reached Luhansk and was unloading 2,000 metric tons of grain, sugar, baby food), medications, sleeping bags and portable power generators, according to an official of the self-proclaimed Luhansk People's Republic.

The report put the size of the convoy at 262 trucks, not the 280 reported by the Ukrainian government.

"Unloading of humanitarian cargoes has started. The cargoes will then be distributed among residents," an unnamed city official said. Itar-Tass added that he did not rule out that some of the aid would be sent to Donetsk, another self-declared People's Republic.

NATO Secretary General Anders Fogh Rasmussen condemned Russia for sending the unauthorized humanitarian aid convoy into Ukraine on Friday without the involvement of the International Committee of the Red Cross. The Kiev government called the advance by an estimated 280 Russian trucks into Ukrainian territory a "direct invasion."

Rasmussen, who recently visited Ukraine, said in a statement from Brussels that Russia's "blatant breach" of its international commitments "can only deepen the crisis in the region, which Russia itself has created and has continued to fuel."

"These developments are even more worrying as they coincide with a major escalation in Russian military involvement in Eastern Ukraine since mid-August, including the use of Russian forces," he added. "In addition, Russian artillery support â?? both cross-border and from within Ukraine â?? is being employed against the Ukrainian armed forces."

He said large quantities of advanced weapons, including tanks, armored personnel carriers, and artillery.had been transferred recently to separatist groups in eastern Ukraine.

"Moreover, NATO is observing an alarming build-up of Russian ground and air forces in the vicinity of Ukraine," Rasmussen said.

NATO spokeswoman Oana Lungescu said the Western alliance had received numerous reports of the direct involvement of Russian forces, "including Russian airborne, air defense and special operations forces in eastern Ukraine," The New York Times reported.

"Russian artillery support - both cross-border and from within Ukraine - is being employed against the Ukrainian armed forces," she said.

The NATO warnings come as Ukrainian troops have begun to gain ground against Russian-backed separatists in their battles over the disputed area since April.

Russian President Vladimir Putin and Ukrainian President Petro Poroshenko are scheduled to meet next week in Minsk, Belarus, on the sidelines of a regional economic summit, to discuss the instability in Ukraine.

The controversial Russian aid convoy left Moscow Aug. 12 with 2,000 tons of humanitarian aid, including baby food, medicine, grain, sugar, sleeping bags and other items, Russia's government-run RIA Novosti reports. The vehicles, covered with white tarps, have been stuck at a border crossing in a dispute between Russia and Ukraine over inspection of the vehicles.

Several of the trucks on Friday reached the besieged city of Luhansk, which has been without water or electricity for several weeks.

The Russian foreign ministry, in a statement on its web site, said Russia took unilateral action to get the convoy moving and accused Ukraine of deliberately delaying the aid. "The Russian side has decided to act," the foreign ministry said.

Only 34 Russian vehicles had received initial approval from Ukraine on Thursday to proceed but were awaiting a final green light. Ukraine had refused to allow the vehicles to cross without inspection and said it would allow them to proceed with only a single driver per vehicle aboard, not a team.

An Associated Press reporter saw a priest blessing the first truck in the convoy at the rebel-held checkpoint and then climbing into the passenger seat. A rebel commander on the scene said 34 trucks had gone through. On the Russia side of the border, an AP reporter counted another 32 vehicles going into the customs zone.

Ukraine had insisted that the Red Cross oversee the distribution of the goods.

The ICRC said on Twitter Friday that it did not join the convoy because of the "volatile security situation."

"We've not received sufficient security guarantees from the fighting parties," the ICRC said. "Our team in Luhansk reports heavy shelling overnight."

Ukraine has been wary of the convoy, fearing it could be a cover for direct Russian military action in support of the rebels. The process has been complicated by the fact that Russia chose to cross the border at a checkpoint controlled by separatists.

The Red Cross has inspected many of the trucks, which carry water, generators and sleeping bags, among other relief items.

In Kiev, Valentyn Nalyvaichenko, chief of the Security Service of Ukraine (SBU), blasted what he called a "direct invasion, under the cynical cover of the Red Cross these are military vehicles with cover documents."

Nalyvaichenko said the truck drivers are military men trained to drive combat vehicles. He claimed that half-empty trucks will be used to transport weapons to the rebels and take the bodies of Russian fighters away from eastern Ukraine.

Ukraine's foreign ministry charged that its border and customs service had begun clearing the main Russian aid convoy Friday morning when it was blocked by Russian forces from inspecting other vehicles in the column.

The foreign ministry said sending vehicles into Ukraine without authorization "indicates deliberate and aggressive nature of Russia's actions."

The Ukraine foreign ministry said Kiev had issued instructions for "the safe passage of the convoy," but warned of the danger of a deliberate provocation by "terrorists" along the way.